Those 100 series cabinets are expensive and loaded with G12H30s normally. New they are $1400 each. The cab is a fair deal at 900.
The head depends on the year. I also would request they open it up and look inside to see the condition and what’s been done to it, no way I’d buy a stock vintage Marshall not knowing what it looks like inside unless your intentions are to mod the hell out of it and not preserve it.